Abstract: The mesoscale numerical model for Ultra-High Performance Cementitious Composites (UHPCC) was developed based on the Finite-Discrete Element Method (FDEM). The material heterogeneity was incorporated in the model, using cohesive elements to characterize the interfacial properties between distinct material phases. Split Hopkinson Pressure Bar (SHPB) tests and penetration experiments were conducted to investigate the crack propagation and failure mechanisms of UHPCC under impact loading from both macroscopic and mesoscale perspectives. The results show that the mesoscale numerical model is in good agreement with the experimental results. A model of randomly distributed fibers is integrated into the FDEM framework, enabling precise discretization of critical regions within the material, effectively capturing the heterogeneous characteristics and reproducing the crack initiation and propagation processes. Cohesive elements serve as bridges between different phases, accurately representing potential fracture surfaces within the matrix. The mechanical response and failure behavior of UHPCC under various impact conditions are accurately predicted by the mesoscale numerical model.